Posted on 02/08/2005 3:50:43 AM PST by PatrickHenry
A group of four-footed mammals that flourished worldwide for 40 million years and then died out in the ice ages is the missing link between the whale and its not-so-obvious nearest relative, the hippopotamus.
The conclusion by University of California, Berkeley, post-doctoral fellow Jean-Renaud Boisserie and his French colleagues finally puts to rest the long-standing notion that the hippo is actually related to the pig or to its close relative, the South American peccary. In doing so, the finding reconciles the fossil record with the 20-year-old claim that molecular evidence points to the whale as the closest relative of the hippo.
"The problem with hippos is, if you look at the general shape of the animal it could be related to horses, as the ancient Greeks thought, or pigs, as modern scientists thought, while molecular phylogeny shows a close relationship with whales," said Boisserie. "But cetaceans – whales, porpoises and dolphins – don't look anything like hippos. There is a 40-million-year gap between fossils of early cetaceans and early hippos."
In a paper appearing this week in the Online Early Edition of the Proceedings of the National Academy of Sciences, Boisserie and colleagues Michel Brunet and Fabrice Lihoreau fill in this gap by proposing that whales and hippos had a common water-loving ancestor 50 to 60 million years ago that evolved and split into two groups: the early cetaceans, which eventually spurned land altogether and became totally aquatic; and a large and diverse group of four-legged beasts called anthracotheres. The pig-like anthracotheres, which blossomed over a 40-million-year period into at least 37 distinct genera on all continents except Oceania and South America, died out less than 2 and a half million years ago, leaving only one descendent: the hippopotamus.
This proposal places whales squarely within the large group of cloven-hoofed mammals (even-toed ungulates) known collectively as the Artiodactyla – the group that includes cows, pigs, sheep, antelopes, camels, giraffes and most of the large land animals. Rather than separating whales from the rest of the mammals, the new study supports a 1997 proposal to place the legless whales and dolphins together with the cloven-hoofed mammals in a group named Cetartiodactyla.
"Our study shows that these groups are not as unrelated as thought by morphologists," Boisserie said, referring to scientists who classify organisms based on their physical characteristics or morphology. "Cetaceans are artiodactyls, but very derived artiodactyls."
The origin of hippos has been debated vociferously for nearly 200 years, ever since the animals were rediscovered by pioneering French paleontologist Georges Cuvier and others. Their conclusion that hippos are closely related to pigs and peccaries was based primarily on their interpretation of the ridges on the molars of these species, Boisserie said.
"In this particular case, you can't really rely on the dentition, however," Boisserie said. "Teeth are the best preserved and most numerous fossils, and analysis of teeth is very important in paleontology, but they are subject to lots of environmental processes and can quickly adapt to the outside world. So, most characteristics are not dependable indications of relationships between major groups of mammals. Teeth are not as reliable as people thought."
As scientists found more fossils of early hippos and anthracotheres, a competing hypothesis roiled the waters: that hippos are descendents of the anthracotheres.
All this was thrown into disarray in 1985 when UC Berkeley's Vincent Sarich, a pioneer of the field of molecular evolution and now a professor emeritus of anthropology, analyzed blood proteins and saw a close relationship between hippos and whales. A subsequent analysis of mitochondrial, nuclear and ribosomal DNA only solidified this relationship.
Though most biologists now agree that whales and hippos are first cousins, they continue to clash over how whales and hippos are related, and where they belong within the even-toed ungulates, the artiodactyls. A major roadblock to linking whales with hippos was the lack of any fossils that appeared intermediate between the two. In fact, it was a bit embarrassing for paleontologists because the claimed link between the two would mean that one of the major radiations of mammals – the one that led to cetaceans, which represent the most successful re-adaptation to life in water – had an origin deeply nested within the artiodactyls, and that morphologists had failed to recognize it.
This new analysis finally brings the fossil evidence into accord with the molecular data, showing that whales and hippos indeed are one another's closest relatives.
"This work provides another important step for the reconciliation between molecular- and morphology-based phylogenies, and indicates new tracks for research on emergence of cetaceans," Boisserie said.
Boisserie became a hippo specialist while digging with Brunet for early human ancestors in the African republic of Chad. Most hominid fossils earlier than about 2 million years ago are found in association with hippo fossils, implying that they lived in the same biotopes and that hippos later became a source of food for our distant ancestors. Hippos first developed in Africa 16 million years ago and exploded in number around 8 million years ago, Boisserie said.
Now a post-doctoral fellow in the Human Evolution Research Center run by integrative biology professor Tim White at UC Berkeley, Boisserie decided to attempt a resolution of the conflict between the molecular data and the fossil record. New whale fossils discovered in Pakistan in 2001, some of which have limb characteristics similar to artiodactyls, drew a more certain link between whales and artiodactyls. Boisserie and his colleagues conducted a phylogenetic analysis of new and previous hippo, whale and anthracothere fossils and were able to argue persuasively that anthracotheres are the missing link between hippos and cetaceans.
While the common ancestor of cetaceans and anthracotheres probably wasn't fully aquatic, it likely lived around water, he said. And while many anthracotheres appear to have been adapted to life in water, all of the youngest fossils of anthracotheres, hippos and cetaceans are aquatic or semi-aquatic.
"Our study is the most complete to date, including lots of different taxa and a lot of new characteristics," Boisserie said. "Our results are very robust and a good alternative to our findings is still to be formulated."
Brunet is associated with the Laboratoire de Géobiologie, Biochronologie et Paléontologie Humaine at the Université de Poitiers and with the Collège de France in Paris. Lihoreau is a post-doctoral fellow in the Département de Paléontologie of the Université de N'Djaména in Chad.
The work was supported in part by the Mission Paléoanthropologique Franco-Tchadienne, which is co-directed by Brunet and Patrick Vignaud of the Université de Poitiers, and in part by funds to Boisserie from the Fondation Fyssen, the French Ministère des Affaires Etrangères and the National Science Foundation's Revealing Hominid Origins Initiative, which is co-directed by Tim White and Clark Howell of UC Berkeley.
I don't know.
I don't want nonsense taught in schools as science.
I don't want the Gospel taught as creationism.
Those are two important issues. If you don't care about them one way or another, don't disparage those that do care.
How Christian of you to ridicule someone that tried to teach you some biology.
How about some facts refuting evolution instead of petulant scoffing?
One of the most difficult problems facing those who accept the naturalistic origin of life is that the odds are against the chance formation of even the most simple organic molecules. The hormone, vasopressin, is a simple protein— simple as far as proteins are concerned. Vasopressin produced in the pituitary gland, prevents the loss of too much water in the body by regulating the action of the kidneys. Further, it increases a person’s blood pressure.
Chemically, vasopressin is made up of eight amino acids. These are, in order along the molecule glycinamide, arginine proline cystine asparagines, glutamine, phenylalanine, and tyrosine. The order in which these amino acids occur is extremely critical to the proper functioning of the hormone Even a switch in position between two amino acids along the molecule will destroy the correct function.
If we were to place just these eight amino acids in a hat and draw them all out one by one, we could expect to get them in the same order as they are in vasopressin only 1 out of every 40,320 attempts The reason is simple. When you draw out the first amino acid, there are eight possibilities. For the second choice, there are seven amino acids in the hat so there are only seven possibilities etc. Thus, the number of possibilities for the “vasopressin type” of hormone is 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1. This equals 40,320.
The number of possibilities increases dramatically as the protein molecule gets larger. Isaac Asimov* estimates that the 30 amino-acid-protein, insulin, has 8,000,000,000,000,000,000,000,000,000 (eight octillion) different arrangements. He further estimates that the number of possible combinations for a 140 amino acid protein like hemoglobin is 135 followed by 165 zeroes. This is a larger number than all the atoms estimated in the universe.
Out of all these possibilities, the body can use only one arrangement. Asimov states, "Out of 40,320 possible vasopressin combinations, the body chooses just one out of eight octillion possible combinations; for one of the insulin polypeptides, the body chooses just one."
"The question is no longer where the body finds the variety it needs, but how it controls the possible variety and keeps it within bounds."**
*Isaac Asimov, The Genetic Code, New York: The New American Library, 1962, p. 92.
**lbid., p.93.
Are you saying that it is possible all life may not have a common ancestor?
$$ to doughnuts you wont say you agree with evolution ...
Evolution is not taught, people are indoctrinated to evolution.
A very quibbling point, but I don't think you need to (or should) distinguish solid facts from revisable scientific theories. In science facts are also revisable. The most basic fact is simply a well confirmed observation, and it's necessary to hold open the possibility that it may be disconfirmed by future observations, for example because of improved instruments or methods. For instance the number of human chromosomes was miscounted for years and this was corrected, I believe, by better stains and staining techniques.
I don't disparage you for caring, I disparage you for belittling people and being poumpous and arrogant in your defenses of your positions.
Three out of 50 is "so many"?
Good work debunking the bogus George Wald quote.
I don't want the Gospel taught as creationism.
The same Bible that gives us the Gospel also tells us that God created life. Next thing you will be telling us that God didn't make an ax head float or cause the sun to stand still.
Or raise His Son from the dead.
How many more?
Leviticus 11:10 But anything in the seas or rivers that does not have fins and scales, regard as an abomination. Do not eat their meat and regard their carcasses as an abomination.
Please go reread Evolution 101.
Science does not deal in "proof". Anyone that asks for proof is not a scientist....
That is absolute NONSENSE!
Are you saying that the mathematical proof needed in physics, engineering, quantitative chemistry, etc, etc.. is not science?
It's a hell of a lot more proof and true exact science than a bunch of conjectures, suppositions and strech of the imagination based on a few bones and some theory.
My facts have put a man on the moon, your "facts" for linking a whale and a hippo are "a similarity in DNA?"
You give me a link to a paper that repeatedly tells me that EVOLUTION IS A FACT and that anyone who doubts it is ignorant. BUT YOU DO NOT GIVE ME THE PROOF.
When I calculate something to be a pressure of 22.5psi. I can show you the math and the result is always 22.5psi, not 21 or not 23.
I was(politely)trying to tell you that you have not given me the proof that evolution is a fact. Repeating that some people believe that theory to be a fact does not make it so for me.
PMFJI. It's hard not to disparage people and be a bit pompus in these crevo threads. There are just so many creationists out there who spout the same tired stuff and refuse to acknowledge that they have been shown to be wrong time after time after time.
It gets a bit old after awhile.
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